In the memo, Smisek says "we have made the difficult decision to substantially reduce our flying from Cleveland. We will make this reduction in stages beginning in April."

"Our hub in Cleveland hasn't been profitable for over a decade, and has generated tens of millions of dollars of annual losses in recent years," Smisek adds in the letter. "We simply cannot continue to bear these losses."

Smisek said United would reduce its number of daily Cleveland flights by about 60%, keeping most of its "mainline" flights at Cleveland but slashing about 70% of those flown by the company's United Express regional partners.

Once all of the cuts are phased in by June, United's Cleveland schedule will drop from about 199 daily departures to 72.

United will still operate seven mainland U.S. hubs without Cleveland. They are Chicago O'Hare, Denver, Houston Bush Intercontinental, Los Angeles, Newark Liberty, San Francisco and Washington Dulles.

In a sliver of good news for Cleveland, the city will have more nonstop routes and flights on United than a typical non-hub city -- even after the cuts. But Smisek said those will be aimed at passengers heading to or from Cleveland, not at connecting passengers.

United will continue to offer nonstop flights between Cleveland and 20 destinations, flying to its seven remaining hubs and 14 other cities. That's down significantly, however, from the 61 nonstop destinations that United and its United Express affiliates currently serve from Cleveland, according to The Plain Dealer of Cleveland.

Smisek said the remaining Cleveland nonstop routes will include "key business markets" -- like Boston, New York LaGuardia and Washington Reagan National -- as well as "key leisure markets," such as the Florida cities of Fort Lauderdale, Fort Myers, Orlando and Tampa.

Cleveland had long been a hub for Continental Airlines. But it also had been the subject of speculation among industry observers about whether it would survive over the long haul in the same role for United, which inherited the hub in the 2010 merger with Continental.

Now, Cleveland will join cities like Columbus, Las Vegas, Memphis, Milwaukee, Pittsburgh and St. Louis that have seen big U.S. airlines dismantle connecting hubs in their cities since 2003.

"Ever since the merger everyone knew this was a risk, which is why economic development officials for the city, the region and the state have discussed options with United for keeping its presence in Cleveland," Ohio Gov. John Kasich is quoted as saying by The Associated Press. "This is a disappointing decision and one we disagree with, but a point that United stressed is that demand for air travel from Cleveland remains strong and that they're maintaining virtually all of their flights to and from major markets."